Furnace



2 mmf@ INVENTOR H. LARMAN 2,480,374

FURNACE 4 Sheets-Sheet 1 J BY MMM

ATTORN EY Aug. 30, 1949.

Filed Sept. 20, 1945 H. LARMAN Aug. 30, 1949.

FURNAGE 4 Sheets-Sheet 2 Filed Sept. 20, 1945 tud, I

INVENTOR. Harry Lamm/2 BY .rmfa

v H. LARMAN Aug. 30, 1949.

FURNACE 4 Sheets-Sheet 4 Filed Sept. 20, 1945 y IN V EN TOR. Har/y L arman Bzwa Patented Aug. 30, 1949 FURNACE Harry Larman, Gary, Ind., assignor to Carnegie- Illinois Steel Corporation, a corporation of New Jersey Application September 20, 1945, Serial No. 617,622

8 Claims.

This invention relates to an improved furnace and more particularly to a batch type furnace for use in heating charges of materials. The furnace of the invention may be used in heating a variety of objects, but displays perhaps its maximum advantages in heat treating operations, such as the annealing or carburizing of metal.

Among the objects of the invention is the provision of a simple efcient furnace which allows the heating of material in a fast, very uniform manner.

Another object of the invention lies in the provision of a furnace by which the entire surface of the material being heated can be brought up to the required temperature at substantially the same time Without requiring retarding of the firing rate.

A further object resides in the provision of furnace which provides an even soaking and heat penetration into the material being heated,

thereby resulting in the uniform overall quality of such material and the minimizing of the soaking time required. As a result the temperature of the material can be brought up fast Without injury thereto and without creating defects therein, such as cracks or warpage through stresses caused by temperature diiferentials.

These and further objects of the invention will be more readily apparent in the following description.

The majority of fuel operated, stationary, heat treating furnaces heretofore employed for use in operations such as annealing and carburizing of metal are designed for convection and hearth conduction heating. Such furnaces require a retarded heating speed to insure uniformity of heating throughout the mass of the article or articles being heated, and are therefore slow and inefficient in operation. Typical of such furnaces is the conventional hood type annealing furnace having a hearth upon which the material being heated is supported, a plurality of down draft waste gas flues and horizontal combustion flues spaced longitudinally therethrough.

` The removable hood which fits over the hearth carries a plurality of burners so spaced as to match and direct their flames into the combustion fiues of the hearth, thereby providing slow indirect heating by conduction through the hearth. Since combustion is almost completed at the outlets of the combustion flues, very little heat transfer is obtained by flame radiation. Moreover intense hot spots will develop in the hearth adjacent to the burner ends of the combustion fiues. As a result the heating of the charge is slow, inefficient and non-uniform.

The heating furnace of the present invention overcomes such difculties by so locating the burners relative to the charge that the charge is covered by a substantially uniform blanket of name over the top thereof and also along the sides and ends. Direct heating of the hearth by the flames is obviated, heating of the charge being mainly accomplished by such blanket of ame which transfers its heat to the charge by flame radiation in addition to convection.

The invention will be more readily understood by reference to the accompanying drawings, in which:

Figure 1 is a view in longitudinal vertical section through one type of furnace embodying the present invention, the section being taken along the line I-I of Figure 3;

Figure 2 is a View in transverse vertical section through the furnace shown in Figure l, the section being taken along the line II-II in Figure 1;

Figure 3 is a view in horizontal section through the furnace shown in Figures 1 and 2, the section being taken along the line III-III of Figure 1;

Figure 4 is a. schematic view of the burners and the piping supplying such burners in the furnace shown in Figures 1, 2, and 3;

Figure 5 is a view in longitudinal vertical section through a modification of the furnace of the present invention, the section being taken along the line V-V in Figure 7;

Figure 6 is a View in transverse vertical section through the furnace shown in Figure 5, the section being taken along the line VI-VI of that gure; and

Figure 7 is a view in horizontal section through the furnace shown in Figures 5 and 6, the section being taken along the line VII-VII in Figure 5.

In the furnace shown in Figures 1, 2, and 3, blanketing of the end of the charge by the names is accomplished by the burners on the upper portion ofthe side walls of the furnace hood operating in conjunction with those directing flames along the sides of the charge. In the modification shown in Figures 5, 6, and 7, which is preferable in some cases where more complete blanketing at the ends of the charge is desired, additional burners are supplied directing blanketing flames along the ends of the charge.

As shown in Figures l, 2, and 3, the furnace consists of a furnace hood 2 having a metal shell and a refractory lining, as shown, the hood fitting over the hearth 4, as shown in Figures 1 and 2,

to provide appreciable spaces between the inner side surfaces of the hood and the sides of the hearth. The lower edges of the sides and ends of the hood and the portions of the hood supporting structure around the'hearth are provided with a sealing means, such as a. conventional sand seal 6, which substantially excludes air from the furnace interior and allows the furnace to be operated under a substantial pressure.

The top of the hearth 4 is provided with a plurality of spaced, parallel, charge supporting beams or skids 8 upon the upper surfaces of which the charge may rest. Beneath lthe hearth there is provided the horizontal stack I with which the vertical -waste gas ducts I2 communicate, ducts I2 extending through the hearth and being spaced substantially equal distances longitudinally thereof. The-furnace hood is provided at each end thereof with two lower burners', designated I4 at the right hand end in Figures 1 and 3, and I6 at the left hand end of Figures 1 and' 3, such burners being located at an elevation well below the upper charge supporting surfaces of skids 8 and \in the furnace shown also below lthe top of hearth 4. The burners I4 and I6 are located in line with the spaces I5 and I1, shown at the right and left' hand sides of Figure 2, respectively, between the side wall of the hood and the vertical side of the hearth confronting such hood side walls. Flames from the burners I4 and I6 are therefore projected into the furnace interior along the side walls of the furnace hood and thus tend to form a' blanket over the side surfaces of the furnace charge.

The furnace hood is also provided with a series of burners on each upper side wall thereof providing a blanket of flame over the top of the charge. Such upper burners on the right hand side of Figure 2 and the lower side of Figure 3 are designated I8 and those at the left hand side of Figure 2 and the upper side of Figure 3 are designated 20. -Burners I8 and 28 lie in a common horizontal plane, burners I8 being spaced substantially equal distances along one side of the hood, as shown, and burners 20 being spaced substantially equal distances along the other side. Burners I8 are staggered with respect to burners 20, as shown in Figure 3, so that each burner I8 lies substantially midway between each adjacent pair of burners 20.

Flames from the upper burners I8 and 20 travel in the paths indicated by the arrows in Figures 2 and 3. As there indicated the ames travel in a substantially horizontal direction over the top of the charge, which ordinarily does not extend above the level of burners I8 and 20, so that the llames do not impinge directly upon it. After reaching the other side of the furnace the flames and hot gases travel downwardly into the adjacent waste gas flue I2, where with'the gases from the lower burners I4 and I 6 they are drawn into the exhaust stack I0, such path of travel, when the charge consists of separate coils or stacks of articles being heated, being through such charge. Because 'of the staggered relationship of burners I8 and 20, there is formed a substantially uniform blanket of iiame, as indicated in Figure 3, above the charge. Such blanket will also extend over the ends of the charge toa certain degree so that for all practical purposes the charge is completely covered on its top, side, and end surfaces by a blanket of flame. The burners, which may be of a simple inspirating type burning either gaseous or liquid fuel, may be supplied with fuel in the manner indicated in Figure 4. Fuel. -which in this instance will be assumed to be gaseous, isfintroduced through gas main 22 having an automatic regulating valve 24 therein, into the lower header 26 for the bottom burners. Gas to the upper header 28 for the top burners is supplied from the lower header through the medium of the branch line between the headers. Bottom burners I4 are supplied from the lower header by means of the gas lines 32 and the burners I6 are supplied from the lower header by gas lines 34. Upper burners I8 are supplied from the upper header by means of gas lines 38 and burners 20 are supplied in the same manner by lines 88. Each gas line feeding each individual X burner is equipped with a manually operated valve, as shown, to aid initial adjustment of the burners. It is generally unnecessary, however, once the proper balance is secured between burners, to vary such individual valves, although occasionally the type of charge being heated may require such adjustment to secure uniformity of heating. The valves 52 and 54 are positioned in header 28 on either side of the connection of branch line 30 so as to divide the furnace into zones. This makes it possible to adjust and control is especially desirable in the case of uneven charging of the furnace so that the entire charge can be brought up to temperature simultaneously. Automatic controls for valves 52 and 54 are desirable but since periodic adjustment should be sufiicient, manual operation would be practical and satisfactory. Automatic control valve 24, which may be of one of numerous known types, functions to control the volume of fuel fed to the furnace and thus to maintain the desired furnace temperature. Valve 24 may be automatically controlled by means of thermocouples located in the furnace interior.

In instances where it is desired that the ends of the charge shall be more completely and `uniformly blanketed with flames than is possible by the use of the furnace above described, the modification shown in Figures 5, 6, and 7 may be employed. The furnace shown in such latter gures is generally similar to that in Figures 1, 2, and 3, and similar parts are designated by the same reference characters. The differencev between the modification lies in the provision of additional burners at the lower portion of the furnace for directing flames along the ends of the charge. In such furnace, the hood is so made relative to the hearth that there are spaces between the ends of the hearth and the inner surfaces of the ends of the hood as well as between the sides of the hearth and the inner surfaces of the sides of the hood. Such space at the right hand end of Figures 5 and 7 is designated 40, rand that between the end of the hearth and the end wall of the hood at the left hand end of Figures 5 and 7 is designated 42. 'I'he furnace hood is provided on the lower portion of its side walls and in locations aligned with spaces 40 and 42- with lower end burners, those at the right hand end of Figures 5 and 7 being designated 44 and those at the left hand end of such figures being designated 46. Such burners, which are preferably located slightly above the lower side blanketing burners I4 and I6 to avoid interference between the ames issuing therefrom, are located at a level Well below the top surfaces of the skids 8 to insure complete blanketing of the end surfaces of the charge. End burners 44 are supplied, as shown. through gas lines 48 likewise equipped with individual valves. and burners IB dividually adjustable valves. Flames from burners 44 and 46 travel lengthwise for some distance through spaces 40 and 42, respectively, and thence rise to blanket the ends of the charge. Such flames and hot gases mingle over the top of the charge with the flames and gases from the upper burners and the side burners, and thus proceed, in the manner above described, downwardly to the waste gas flues.

As a result of the structure of the furnace in either of the modifications described, a notable increase in efficiency of heating has been secured and the heating cycle has been very greatly shortened. In addition, rejection of heat treated articles has been very greatly lessened due to the great uniformity of heat treatment secured in such furnace. Such results are explained by the lack of direct flame impingement upon any part of the charge and the fact that the charge is covered by a substantially uniform blanket of radiant flame. Radiation from such flame, plus flame convection, provide an early incandescence to the roof and walls, thereby continuously increasing the heat radiation to the charge. In addition, all gases of combustion are drawn down through the charge to the stack, thereby giving up additional heat by convection to the charge and insuring a low stack temperature, which is indicative of high emciency in heating.

Having thus fully disclosed preferred constructions and arrangements for furnaces embodying the present invention and the manner in which they operate, I desire to claim as new the following:

1. A heating furnace comprising a hearth for supporting the charge being heated, an enclosure for the charge above the hearth, a series of burners spaced longitudinally along the upper part of opposite sides of the enclosure to direct llames therewithin in opposite directions above the charge to form a blanket of flame thereabove, a plurality of burners in the vicinity of the hearth directing names longitudinally of the furnace to form a blanket of flame over the sides of the charge, said ilrst and second named burners being situated where their flames avoid impinging against the charge but where heat from their flames can radiate directly on the surfaces of the charge, a plurality of waste gas ues in the hearth spaced longitudinally thereof, said flues being situated where substantially all the products of combustion are drawn through the charge, and an exhaust stack to which the waste gas flues are connected.

2. A heating furnace comprising a hearth, means for supporting the charge being heated on the hearth, an enclosure for the charge above the hearth, means forming a seal between the hearth and the enclosure, a series of burners substantially equally spaced longitudinally along the upper part of opposite sides of the enclosure to direct flames therewithin in opposite directions above the charge to form a blanket of flame thereabove, a plurality of burners located below the top charge supporting surface of the charge supporting means directing flames longitudinally "f the furnace along the side walls thereof to form a blanket of flame over the sides of the charge, said first and second named burners being situated where their flames avoid impinging against the charge but where heat from their flames can radiate directly on the surfaces of the charge, a plurality of waste gas ues in the hearth spaced longitudinally thereof, said flues being situated where substantially all the products-of combustion are drawn through the charge, and an exhaust stack to which the waste gas ues are connected.

3. A heating furnace comprising a hearth for supporting the charge being heated, an enclosure for the charge above the hearth, means forming a seal between the hearth and the enclosure. the hearth projecting a substantial distance within the enclosure and the side walls of the enclosure being spaced a substantial distance from the sides of the hearth along opposite sides thereof, a series of burners substantially equally spaced longitudinally along the upper part of vsaid opposite sides of the enclosure to direct flames therewithin in opposite directons above the charge to form a blanket of flame thereabove, a plurality of burners located on the enclosure end walls in the vicinity of the spaces between the sides of the hearth and the sides of the enclosure below the top of the hearth for directing flames longitudinally of such spaces and along the side walls of the furnace to form a blanket of flame over the sides of the charge, said first and second named burners being situated where their flames avoid impinging against the charge but where heat from their flames can radiate directly on the surfaces of the charge, a plurality of waste gas ilues in the hearth spaced longitudinally thereof, said flues being situated where substantially all the products of combustion are drawn through the charge, and an exhaust stack to which the waste gas flues are connected.

4. A heating furnace comprising a hearth for supporting the charge being heated, an enclosure for the charge above the hearth, means forming a seal between the hearth and the enclosure, the hearth projecting a substantial distance within the enclosure and the side walls of the enclosure being spaced a substantial distance from the sides of the hearth along opposite sides thereof, a series of burners substantially equally spaced longitudinally along the upper part of said opposite sides of the enclosure to direct flames therewithin in opposite directions above the charge to form a blanket of flame thereabove, the burners on one side of the enclosure being staggered relative to those on the other side so that the burners on the ilrst side lie substantially midway between those on the second side, two substantially horizontally directed burners located on each of the enclosure end walls, each such burner being in line with one of the spaces between the sides of the hearth and the sides of the enclosure and below the top of the hearth for directing flames longitudinally of such spaces and along the side walls of the furnace to form a blanket of flame over the sides of the charge, said first and second named burners being situated where their flames avoid impinging against the charge but where heat from their flames can radiate directly on the surfaces of the charge,

charge to form a blanket of flame thereabove, a plurality of burners in the vicinity of the hearth directing llames longitudinally of the furnace to form a blanket of flame over the sides of the charge, a plurality of burners in the vicinity of the hearth for directing flames laterally of the furnace to form a blanket of flame over the ends of the charge, said first, second and third named burners being situated where their flames avoid impinging against the charge but where heat from their flames can radiate directly on the surfaces of the charge, a plurality of waste gas flues in the hearth spaced longitudinally thereof, said flues being situated where substantially all the products of combustion are drawn through the charge, and an exhaust stack to which the waste gas flues are connected.

6. A heating furnace comprising a hearth, means for supporting the charge being heated on the hearth, an enclosure for the charge above the hearth, means forming a seal between the hearth and the enclosure, a series of burners substantially equally spaced longitudinally along the upper part of opposite sides of the enclosure to direct flames therewithin in opposite directionsV above the charge to form a blanket of flame thereabove, a plurality of burners located below the top charge supporting surface of the charge supporting means directing flames longitudinally of the furnace along the side walls thereof to form a blanket of flame over the sides of the charge, a plurality of burnrs located below the top charge supporting surface of the charge supporting means directing flames laterally of the furnace along the furnace end walls to form a blanket of flame over the ends of the charge, said first, second and third named burners being situated where their flames avoid impinging against the charge but where heat from their flames c an radiate directly on the surfaces of the charge, a plurality of waste gas flues in the hearth spaced longitudinally thereof, said flues being situated where substantially all the products of combustion are drawn through the charge, and an exhaust stack to which the waste gas ues are connected.

7. A heating furnace comprising a hearth for Supporting the charge being heated, an enclosure for the charge above the hearth, means forming a seal between the hearth and the enclosure, the hearth projecting a substantial distance within the enclosure and the walls of the enclosure being spaced a substantial distance from the sides of the hearth along opposite sides and ends thereof, a series of burners substantially equally spaced longitudinally along the upper part of said opposite sides of the enclosure to direct flames therewithin in opposite directions above the charge to form a blanket of flame thereabove, a plurality of burners located on the enclosure end walls in the vicinity of the spaces between the sides of the hearth and the sides of the enclo-,-.

sure belowv the top of the hearth for directing flames longitudinally of such spaces and along the side walls of the furnace to form a blanket of flame over the sides of the charge, a plurality of burners located on the enclosure side walls in the vicinity of the spaces between the ends of the hearth and the sides of the enclosure below v the top of the hearth for directing flames longitudinally of such latter spaces and along the end walls of the furnace to form a blanket of flame over the ends of the charge, said rst, second and third named burners being situated where their ames avoid impinging against the charge but where heat from their flames can radiate directly on the surfaces of the charge, a plurality of waste gas flues in the hearth spaced longitudinally thereof, said flues being situated where substantially all the products of combustion are drawn through the charge, and an exhaust stack to which the waste gas flues are connected.

8. A heating furnace comprising a. hearth for,

supporting the charge being heated, an enclosure for the charge above the hearth, means forming a seal between the hearth and the enclosure, the hearth projecting a substantial distance within the enclosure and the inner surfaces of the sides and ends of the enclosure being spaced a substantial distance from the sides and ends of the hearth along opposite sides and ends thereof, a series of burners -lying substantially in a common horizontal plane and substantially equally spaced longitudinally along the upper partof said opposite sides of the enclosure to direct flames therewithin in opposite directions above the charge to form a blanket of flame tliereabove, the burners on one side of the enclosure being staggered relative to those 0n the other side so that the burners on the first side lie substantially midwayl between those on the second side, two substantially horizontally directed burners located on each of the enclosure end walls, each such burner being in line with each of the spaces between the sides of the hearth and the sides of the enclosure and below the top of the hearth for directing flames longitudinally of such spaces and along the side walls -of the furnace to form a blanket of flame over the sides of the charge, two substantially horizontally directed burners located on each of the enclosure side Walls, each such burner being in line with one of the spaces between the ends of the hearth and the end walls of the enclosure and below the top of the hearth for directing flames longitudinally of such latter spaces and along the end walls of the furnace to form a blanket of flame over the ends of the charge, said first, second and third named burners being situated where their flames avoid impinging against the charge but where heat from their flames can radiate directly on the surfaces of the charge, a plurality of waste gas flues in the hearth spaced substantially equally longitudinally thereof, said flues being situated where substantially all the products of combustion are drawn through the charge, and an exhaust stack to which the gas flues are connected.

HARRY LARMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,264,961 Moyer May 7, 1918 1,271,364 Ralya July 2, 1918 1,401,054 Delacourt Dec. 20, 1921 1,599,165 Clark Sept. 7, 1926 1,605,630 Watkins Nov. 2, 1926 1,688,393 Manker Oct. 23, 1928 2,194,977 Hoak Mar. 26, 1940`r` 2,196,902 Jones Apr. 9, 1940 2,276,971 Hoak Mar. 17, 1942 2,389,027 Corbin et al Nov. 13, 1945 2,438,812 Loftus Mar. 30, 1948 l M E y Certificate of Correction l Patent No. 2,480,374 .August 30, 1949 HARRY LARMAN It is hereby certified that error appears in the printed specification of the above numbered patent requirmg correct1on as follows:

-Column 4, line 28, after the syllable trol and before is insert the words and y period the rate of heating in each zone. Such control;

and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 17th day of January, A. D. 1950.

[m1-l Y THOMAS F. MURPHY,

Assistant Oommz'ssz'oner of Patents. 

